Fixing MSDTC between two machines on different domains

I’ve been chasing problems with MSDTC today. We were trying to get one machines on a different domain to use MSDTC through COM+ to talk to a remote SQL Server on a different domain.

Select / Read operations seemed to work fine but when it attempted to use an UPDATE method in a transaction, it failed with an exception saying

COM+ was unable to talk to the Microsoft Distributed
Transaction Coordinator (Exception from HRESULT: 0x8004E00F)

The following information describes my eventual journey to success.

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